JP2851124B2 - Multiplex transmission method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multiplex transmission system for transmitting data between multiple nodes connected to a common transmission line.

(Prior art) Conventionally, this type of multiplex transmission system includes CSMA / CD (Carrier
Sence Multiple Acess / Collision Detection) and AMP
(Arbitration on Message Priority)
(Local Area Network) transmission system. For example, a typical example is CAN used for data transmission in automobiles.
(Controller Area Network).

FIG. 10 is a configuration block diagram of the conventional example, in which terminating resistors R _E and R _E are connected to both ends of two transmission lines A and B,
Multiplex nodes 11 to 13 are connected to the transmission lines A and B in parallel. Since the multiplex nodes 11 to 13 have the same configuration, the multiplex node 11 will be described for convenience of explanation.

The multiplex node 11 includes a communication control device 21 and a communication control device 21.
A transmission circuit for receiving a transmission signal from the transmission lines A and B;
And a receiving circuit for transmitting the signal to the receiver.

Receiving circuit, a resistor R ₃ to R _9, the transmission line A, and outputs a signal received from the B to the comparator 21a of the communication control device 21, by providing the appropriate Suresshuhorudo voltage to the comparator 21a, the transmission signal Of the receiving circuit is reduced to an acceptable level, thereby widening the common mode input voltage range of the receiving circuit, thereby making it less likely to be affected by noise.

The transmission circuit includes field effect transistors (FETs) 22 and 23,
The FET 22 is composed of a circuit comprising diodes D ₁ and D ₂ and resistors R ₁ and R ₂ , and the FET 22 is connected to the transmission line A via the diode D ₁ and the resistor R _1.
Connected to, FET 23 is connected to the transmission line B via the diode D ₂ and resistor R _2.

Therefore, when the multi-node 11 is passive, that is, CSMA / C
In the D + AMP transmission method, when the recessive bit is output, the FETs 22 and 23 are both off, and the transmission line A and the transmission line B are in a high impedance state without any potential difference. When the multiplex node 11 is dominant, that is, when it outputs a dominant bit, both the FETs 22 and 23 are on and the transmission line A
And the current from the transmission line B is taken in. For this reason, at the time of dominant, a potential is generated between the transmission lines A and B, and a receiving circuit connected to the transmission lines A and B detects a potential difference, inverts the comparator 21a, and detects a dominant. .

(Problems to be Solved by the Invention) However, in the above-described transmission system, when a failure such as disconnection or short-circuit of one of the transmission lines occurs, the potential between the transmission lines changes, and all of the transmission lines are changed. There is a problem that data transmission between multiple nodes becomes impossible.

The present invention has been made in view of the above problems,
It is an object of the present invention to provide a multiplex transmission system capable of efficiently performing data transmission between multiplex nodes even if a failure occurs on a transmission line.

(Means for Solving the Problems) In order to achieve the above object, the present invention has at least two multiplex nodes connected to each other via a common signal transmission line, and each of the multiplex nodes is any one of the multiplex nodes. In the multiplex transmission system for transmitting predetermined transmission data in response to a transmission request of the multiplex node, the signal transmission line includes at least three signal transmission lines, and each of the multiplex nodes includes at least one signal transmission line among the signal transmission lines. Detecting the voltage of the transmission line, specifying the state of each signal transmission line according to the voltage value, and communicating at least one multiplex node with each of the multiplex nodes to detect a failure, A multiplex transmission method is provided in which the state of each signal transmission line is changed by changing the voltage of the transmission line to perform data transmission between each multiplex node.

(Operation) At least one of the multiple nodes is
When the failure of the signal transmission line is detected, the state of each signal transmission line is changed to a state in which data can be transmitted by changing the voltage of the signal transmission line.

Accordingly, even if a failure occurs due to disconnection or short circuit of the signal transmission line, a predetermined potential is generated between the signal transmission lines, and data transmission between the multiple nodes becomes possible.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings of FIGS.

FIG. 1 is a block diagram showing a configuration of a multiplex transmission system according to the present invention. In the figure, each multiplex node 30, 40,
Reference numerals 50 and 60 are connected to three transmission lines A, B and C, respectively, and transmit data signals between the multiplex nodes. Of the multiplex nodes, the multiplex nodes 30 and 40 connected to other than the end of the transmission line have the same configuration blocks, respectively. explain.

The multiplex node 30 includes a communication control device 31 that performs communication processing control.
A transmission control circuit 32 that receives a transmission signal from the communication control device 31 and sends it out to the transmission line, a reception control circuit 33 that provides a reception signal fetched from the transmission line to the communication control device 31, For example, it comprises a voltage detection circuit 34 that detects the voltage of the transmission line C and notifies the communication control device 31 and the like of the state of the transmission line C.

In addition, the multiplex nodes 50 and 60 connected to the end of the transmission line
Are communication control devices 51 and 6 having the same function as that of the multiplex node 30.
1, transmission control circuits 52 and 62, reception control circuits 53 and 63, and voltage detection circuits 54 and 64, respectively, and transmission lines A and
Terminating circuits 54 and 64 having terminating resistors connected to both ends of B and C are added. Also, the multiplex nodes 50 and 60 connected to the termination unit
For example, a voltage generating circuit 56 for applying a voltage to the transmission line C is added to one of the multiple nodes 50, for example.

Each voltage detection circuit is adapted to circuit configuration as shown in FIG. 2, the one terminal of the voltage comparator circuit CM _1, CM _2, the voltage V ₀ which transmission line C is resistor R ₁₀ and capacitor C ₁₀ and a reference voltage V ₁ , V ₂ obtained by dividing the power supply voltage V _CC by the voltage dividing resistors R _{11 to} R ₁₃ is applied to the other terminal. It is detected whether the voltage value of the transmission line C is within the range of the reference voltages V ₁ and V ₂ . That is, when the voltage V ₀ is within the range of the reference voltage V _1, V ₂ is the output terminal K _1, K ₂ as a normal state "0", "0" is output, respectively, the voltage V ₀ reference When the voltage exceeds the range of the voltages V ₁ and V ₂ , for example, when the transmission line A is broken, “1” and “0” are output to the output terminals K ₁ and K ₂ as abnormal states, respectively.
Also, when the voltage V ₀ exceeds the range of the reference voltages V ₁ and V ₂ , for example, when the transmission lines B and C are short-circuited, “0” and “1” are output to the output terminals K ₁ and K ₂ as an abnormal state. Is output.

As shown in FIG. 3, the transmission control circuit includes FETs 35 and 36, diodes D ₁ and D ₂ and resistors R ₁₄ and R ₁₅ as in the conventional example of FIG.
It is composed of a filter circuit composed of, FET 35 is connected to the transmission line A through a filter circuit comprising a diode D ₁₀ and the resistor R _14, via a filter circuit FET36 is a diode D ₁₁ and a resistor R ₁₅ The transmission signal is transmitted by connecting to the transmission line B.

In the reception control circuit, as shown in FIG. 4, the transmission lines A, B,
A power supply voltage of 1/2 V _CC is applied to C via resistors R ₁₆ , R ₁₇ , and R ₁₈ . Transmission lines A, B, and one end and C, the input terminal of the voltage comparator circuit CM ₃ are connected by the switch terminals S ₁ to S ₄ shown in FIG. The switch elements S _{1 to} S ₄ are on / off controlled by a communication control device, and the communication control device switches the switch elements S _{1 to} S ₄ according to signals input from K ₁ and K ₂ of the voltage detection circuit. On / off control is performed by the combinations shown in Table 1 below. The resistance R ₁₆ to R ₂₃ is the resistance of the voltage divider and Suresshuhorudo voltage setting.

The reception control circuit performs balanced transmission of the transmission line A by positive logic and transmission line B by negative logic when K ₁ and K ₂ are in the normal state of “0” and “0”. Is high, and the transmission line B is received as a dominant when the voltage is low. In the abnormal state where K ₁ and K ₂ are “1” and “0”, the transmission line C is received as a fixed potential line, the transmission line B is received as unbalanced transmission of negative logic, and K ₁ and K ₂ are set to “0”. In the abnormal state of "1", the transmission line C is received as a fixed potential line, and the transmission line A is received as unbalanced transmission of positive logic. In the transmission state, the transmission line C contains almost no high-frequency component of the transmission waveform in any state, and the transmission line C can use a line centered on the transmission lines A and B surrounding the outside. In addition, the cost of the transmission line is not increased because it is equivalent to the conventional two-core shielded line.

Termination circuit 55, as shown in FIG. 5, through a transmission line A, to divide the both ends connected resistors R _E and B to R _E / 2 in the transmission line C, the resistance R ₂₄ of the transmission line C It is configured to be connected to the switch elements S ₅ and S ₆ . The resistor R ₂₄ is sufficiently smaller than the terminating resistor. Switching element S _5, when the K ₁ is "1", also switching element S _6, when the K ₂ is "1", and is configured to turn on, respectively. The terminating circuit 55 is also used in place of the voltage generating circuit 56 of the transmission line C. For example, when it is desired to force K ₁ and K ₂ to “1” and “0” at the multiplex node 50, , when to turn on the switching element S ₅ under the control of the communication control device 51, also forces the K _1, K ₂ "0", like in a state of "1", the switch element S ₆ under the control of the communication control device 51 Turn on.

In this embodiment, the termination circuit 55 and the voltage generation circuit 56
Since There are common in the multi-node 50, a multi-node 50 which controls the transmission status is forcibly K _1, K ₂ "0", "1" to K _1, K ₂ from the state of "0" , To change to the “0” state,
Even if only the voltage generating circuit 56 is controlled, for example,
For a multiplex node that does not control the transmission state and has a termination circuit, K ₁ and K ₂ maintain “0” and “1” as shown in FIG. It is assumed that K ₁ and K ₂ can be forcibly changed to “0” and “0” in the transmission state regardless of the output state of the voltage detection circuit 64 of the multiplex node 60 by transmitting a signal.

Next, the operation of the signal line failure processing by the multiplex node 50 will be described with reference to the flowchart of FIG. Incidentally, in the multiplex node 50, among the switching elements S ₁ to S ₄ shown in Figure 4 is the reception control circuit 53 sets the S _1, S ₄ on and off S _2, S _3, the voltage detection It is assumed that outputs from the circuits K ₁ and K ₂ of the circuit 54 are in a normal state of “0” and “0”.

First, the communication control device 51 determines whether return transmission is possible when a frame of a transmission signal is received, based on whether each reception multiplex node can normally transmit a frame (step 101).

Next, it is determined whether communication with all multiplex nodes is possible by confirming reception of ACK signals from all multiplex nodes (step 102). If communication is possible, K ₁ and K ₂ are set to “ ₁ ”. The normal state of “0” and “0” is maintained (step 103), and the determination of step 101 is performed again.

If transmission is not possible in step 101, or if communication with all multiplex nodes is impossible in step 102, the switch element S ₁ of the reception control circuit 53 shown in FIG.
Of to S _4, the S _1, S ₃ ON, and sets off the S _2, S _4, then forced to turn on the switching element S ₅ of the termination circuit 55,
The _{K 1, K 2 "1"} , changing to the state of "0" (step 104). Voltage of the transmission line C at this time becomes V ₁ or more, connected nodes are all _{K 1 = 1, K 2 =} 0. Then, it is determined whether or not transmission with the reception multiplex node is possible in the same manner as in step 101 (step 105).

Here, if transmission with the receiving multiplex node is possible,
Next, whether communication with all multiplex nodes is possible, step 10
Judgment is made in the same manner as in step 2 (step 106). If communication is possible, K ₁ and K ₂ are maintained at “1” and “0” (step 10).
7), the determination of step 105 is performed again.

If transmission is not possible in step 105, or if communication with all multiplex nodes is impossible in step 106, the switch element S ₁ of the reception control circuit 53 shown in FIG.
Of S ₄ , S ₁ and S ₃ are turned off, S ₂ and S ₄ are set to on, then the switch element S ₅ of the termination circuit 55 is forcibly turned off and S ₆ is controlled to be on, K ₁ and K ₂ are changed to “0” and “1” (step 108). Voltage of the transmission line C at this time becomes V ₂ less, connected nodes are all _{K 1 = 0, K 2 =} 1. And whether transmission with the receiving multiplex node is possible,
A determination is made in the same manner as in step 101 (step 109).

Here, if transmission with the receiving multiplex node is possible,
Next, whether communication with all multiplex nodes is possible, step 10
2 is determined (step 110), and if communication is possible, K ₁ and K ₂ are maintained at “0” and “1” (step 11).
1), the determination of step 109 is performed again.

If transmission is not possible in step 109, or if communication with all multiplex nodes is impossible in step 110, it is determined that the transmission line is not faulty, and the termination circuit 55 is forcibly stopped. By turning off both the switch elements S ₅ and S ₆ , K
_1, the _{K 2 "0", "0} " is returned to the state (step 112), moves the operation to a routine other failure process (step 11
3).

As a result, when K ₁ and K ₂ are in the normal state of “0” and “0”, the multiplex node 50 sets the potential between the transmission lines A and B during the dominant state as shown in FIG. And transmission line A,
The reception control circuit 53 connected to B detects the potential difference,
The communication control device 51 can detect a dominant.
When one of the transmission lines is fixed at a constant voltage, one of the transmission lines is broken, and two of the arbitrary transmission lines are short-circuited, first, the reception control circuit 53 shown in FIG. Of the switch elements S _{1 to} S ₄ shown, S ₁ and S ₃ are turned on, S ₂ and S ₄ are set to off, and then the switch element S ₅ of the termination circuit 55 is forcibly turned on, and K _1, changing to the state of the _{K 2 "1", "0} ", at the time that can be sent in this state, as shown in FIG. 7 (b), the transmission line C, and the potential between the B occur in dominant when The reception control circuit 53 connected to the transmission lines C and B can detect a potential difference, and the communication control device 51 can detect a dominant. In this case, the potential of the transmission line A may be arbitrary. In the case where K ₁ and K ₂ are “1” and “0”, and transmission is impossible, among the switch elements S _{1 to} S ₄ of the reception control circuit 53 shown in FIG. _1, S ₃ off, is set to turn on S _2, S _4, then forced off the switching element S ₅ of the termination circuit 55,
S ₆ is turned on to change K ₁ and K ₂ to the state of “0” and “1”. When transmission is possible in this state, as shown in FIG. A potential is generated between A and C, the reception control circuit 53 connected to the transmission lines A and C detects a potential difference, and the communication control device 51 can detect a dominant. In this case, the potential of the transmission line B may be arbitrary.

FIG. 8 shows another embodiment of the reception control circuit according to the present invention. In this embodiment, three voltage comparison circuits CM _{4 to} CM ₆ are used, and output signals (potential differences) from the respective voltage comparison circuits are provided. In the select circuit SE, and selects the fetched output signal according to the outputs from K ₁ and K ₂ , that is, K ₁ = K ₂ = 0
, The select circuit SE selects the output signal from CM _4, and when K ₁ = 1, selects the output signal from CM ₅ and K ₂
When = 1, an output signal from the CM ₆ can be selected and output to the communication control device. In this case, a plurality of switch elements are not required, and the number of components can be reduced.

FIG. 9 shows another embodiment of the multiplex node according to the present invention. In this embodiment, the communication control device 70 sets the communicable state of each transmission line to K ₁ = K ₂ = 0 and K ₁ = 1. , K ₂ = 1, and outputs the respective states of K ₁ and K ₂ to the reception control circuit 72 and outputs an output signal (potential difference) from the voltage comparison circuit in the reception control circuit 71. Is selected, it is possible to detect an optimal transmission state in which transmission from the transmission control circuit 72 is possible. In this case, the voltage detection circuit becomes unnecessary, the number of components can be reduced, and a node having the voltage detection circuit and a node not having the voltage detection circuit can coexist.

Therefore, in this embodiment, even if a failure occurs in the transmission line, each multiplex node generates a predetermined potential between the transmission lines, enabling data transmission between the multiplex nodes. Multiplex transmission reliability can be improved.

(Effect of the Invention) As described above, the present invention has at least two multiplex nodes mutually connected via a common signal transmission line, and each of the multiplex nodes has a transmission request from any one of the multiplex nodes. In the multiplex transmission method for transmitting predetermined transmission data according to the following, the signal transmission line includes at least three signal transmission lines, and each of the multiplex nodes detects a voltage of at least one of the signal transmission lines. When the state of each signal transmission line is specified according to the voltage value, and at least one multiplex node detects a failure by communicating with each of the multiplex nodes, it changes the voltage of the signal transmission line. Since the state of each signal transmission line is changed to perform data transmission between the multiple nodes, data transmission between the multiple nodes can be efficiently performed even if a failure occurs on the transmission line.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a multiplex transmission system according to the present invention, FIG. 2 is a circuit diagram showing one embodiment of a voltage detection circuit shown in FIG. 1, and FIG. FIG. 4 is a circuit diagram showing an embodiment of a reception control circuit, FIG. 5 is a circuit diagram showing an embodiment of a termination circuit, and FIG. FIG. 7 is a flowchart for explaining the operation of signal line failure processing by the indicated multiplex node, FIG. 7 is a diagram showing the potential of the transmission line in each transmission state, and FIG. 8 shows another embodiment of the reception control circuit. circuit diagram,
FIG. 9 is a block diagram showing a configuration of another embodiment of a multiplex node, and FIG. 10 is a block diagram showing a configuration of a conventional multiplex transmission system. 30, 40, 50, 60 ... multiple nodes, 31, 51, 61, 70 ... communication control circuit, 32, 52, 62, 72 ... transmission control circuit, 33, 53, 63, 71 ...
Reception control circuit, 34, 54, 64… Voltage detection circuit, 55, 65…
Terminating circuit, 56: Voltage generating circuit, A, B, C ... Transmission line.

Claims (2)

(57) [Claims] 1. A communication system comprising at least two multiplex nodes interconnected via a common signal transmission line, wherein each of the multiplex nodes transmits predetermined transmission data in response to a transmission request from one of the multiplex nodes. In the multiplex transmission system, the signal transmission line includes at least three signal transmission lines, and each of the multiplex nodes detects a voltage of at least one of the signal transmission lines, and outputs each signal in accordance with the voltage value. When the state of the transmission line is specified, and at least one multiplex node communicates with each of the multiplex nodes and detects a failure, the voltage of the signal transmission line is changed to change the state of each signal transmission line. A multiplex transmission system characterized by performing data transmission between each multiplex node by changing the multiplex node. 2. Each of the multiplex nodes has receiving means for receiving a potential of a predetermined signal transmission line pair out of at least three signal transmission line pairs, and reception is impossible due to failure of the signal transmission line. 2. The multiplex transmission system according to claim 1, wherein said predetermined pair of signal transmission lines is switched to another combination.